Why is a square foot not 0.3048 square metres?

Because area scales with the square of the length. The factor is 0.3048², which is 0.09290304 — using the linear factor is the single most common conversion mistake.

4,840 square yards, or 43,560 square feet — about 4,047 m². It began as the area one man with one ox could plough in a day, which is why it is not a round number.

How do I work out the area of a room to convert?

Multiply length by width in the same unit. For rooms that are not rectangular, split them into rectangles, work out each one, and add the results.

Conversions

Area Converter

Enter an area in any unit to see it in all the others at once.

Worked example

A 1,500 sq ft floor in square metres

1 ft = 0.3048 m, so 1 ft² = 0.09290304 m²
1500 × 0.09290304 = 139.35 m²

Where this goes wrong

Using the linear factor on an area

A square metre is not 3.28 square feet, it is 3.28 squared — about 10.76. Areas scale with the square of the linear factor, so anyone converting a floor with the length conversion in their head is out by a factor of three, and usually orders far too little.

Questions

Why is a square foot not 0.3048 square metres?: Because area scales with the square of the length. The factor is 0.3048², which is 0.09290304 — using the linear factor is the single most common conversion mistake.
How big is an acre?: 4,840 square yards, or 43,560 square feet — about 4,047 m². It began as the area one man with one ox could plough in a day, which is why it is not a round number.
How do I work out the area of a room to convert?: Multiply length by width in the same unit. For rooms that are not rectangular, split them into rectangles, work out each one, and add the results.